Pycnomerus rairua, Porch & Smith & Greig, 2020

Porch, Nick, Smith, Tessa R. & Greig, Kelly, 2020, Five new Pycnomerus Erichson (Coleoptera: Zopheridae: Pycnomerini) from Raivavae, French Polynesia, Zootaxa 4718 (2), pp. 239-250 : 243-245

Pycnomerus rairua sp. nov. Porch & Greig

( Fig.1 , 3 )

Type Locality: Raʹirua Swamp, 0.8 km E. of Raʹirua, at 23°52.115’S 147°40.718’W.

Type material. Holotype. French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, DA4 cores, 180– 185 cm depth—prothorax, dorsally and ventrally complete except for appendages. BPBM, Honolulu.

Diagnosis. The relatively square shape, combined with a high density of deep, rounded, close, and relatively evenly distributed punctures distinguishes this species from the others known from the region.

Description. Based on holotype only.

Colour: Piceous black.

Prothorax longer than wide, the greatest width at about 1/2 of pronotal length. Lateral margins slightly but evenly arcuate, without sinuation to basal angles. Lateral margin weakly crenulate with narrow raised border narrower than adjacent marginal sulcus. Lateral sulcus, shallow, very narrow and crenulated by punctures. Anterior angles obtuse to almost right-angled and very slightly produced. Anterior margin very weakly biarcuate to anterior angles, unbordered. Posterior angles marked but obtuse, posterior border arcuate, raised, and sparsely punctate, wid- er than lateral margins. Basal sulcus evenly developed and crenulated by discal punctures. Pronotal disk flattened over medial third, moderately declivous to lateral margins and weakly declivous to anterior and posterior margins. Densely punctate with circular crater-like punctures. Punctures spaced by less than one quarter to one times their own width, closer in middle and more widely spaced posteriorly. Punctures adjacent medially where some coalesce into weakly developed longitudinal rows on either side of weak impunctate medial line, behind middle. Punctures shallower and smaller anteriorly, continuous to margin. Surface between punctures without obvious microsculpture, weakly to moderately shining. Short, pale yellow, setae remaining in some punctures.

Prosternum densely punctate with circular crater-like punctures separated by less their own width, larger in middle and smaller and more widely spaced towards margins. Punctures on prosternal process closer, some adjacent. Anterior with impunctate margin that extends across prosternum. Prosternal process wide (2 times coxal width), raised between coxae and moderately divergent until abrupt postcoxal expansion.Apex of prosternal process slightly angularly emarginate. Hypomera punctate.

Physical dimensions and Ratios.

Pronotum measurements. Pronotum length: 0.97 mm. Pronotum width: 0.92 mm. Anterior width of pronotum: 0.75 mm. Medial width of pronotum: 0.90 mm. Basal width of pronotum: 0.77 mm. Lateral length of pronotum: 0.86 mm. Pronotum length/width ratio: 1.05.

Prosternum measurements. Prosternum length: 0.64 mm. Length prosternum in front of coxae: 0.41 mm. Anterior foramen: 0.61 mm. Basal foramen: 0.58 mm. Prosternal process intercoxal width: 0.25 mm. Maximum prosternal process width: 0.37 mm. Ratio of Prosternal length/Length in front of coxae: 1.56.

Distribution. Known only from Raʹirua swamp, Raivavae, and likely to be a Raivavae endemic. Potentially ex- tinct: material known from other Austral Archipelago islands (Tubuai, Raivavae and Rapa) and nearby Cook Islands (Mangaia and Atiu) represent different taxa.

Etymology. Named for the Raʹirua region of Raivavae where the species was found in the sediments of the swamp we refer to as Raʹirua swamp.

Associated (non-type) material (4 prothoraces not included in type series): French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, RAI 16-2 2016 cores, 150–200cm depth—1 prothorax, dorsally and ventral- ly complete except for appendages. BPBM, Honolulu. French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, RAI16.2 2016 core, 150–200cm depth—3 incomplete prothoraces. Porch research collection.

Comments. We have chosen not to place the four non-type specimens in the type series because there is some variation in shape and puncture density, which may at least partly reflect the relatively poor preservation of several of the specimens, but could imply more than one species is represented in this material. In this instance we choose to be cautious pending the accumulation of more subfossil or modern material which would help resolve this issue.

Figures

FIGURE 1. Holotypes. Pycnomerus raivavae articulated prothorax and head, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, RAI16-2 2016 cores, 150–200 cm depth). Pycnomerus rairua prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, DA4 cores, 180–185 cm depth). Pycnomerus vavitu prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua Swamp, DA4 2008 core, 170–175 cm depth). Pycnomerus mahanatoa prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua Swamp, DA4 2008 core, 205–210 cm depth). Pycnomerus taralewisae prothorax, dorsal (top) and ventral (bottom)—(French Polynesia, Austral archipelago, Raivavae, Raʹirua swamp, DA4 cores, 245–250 cm depth). Scale bars = 0.5 mm

FIGURE 3. Dorsal and ventral views of prothoraces of P. rairua ‘HT’ and associated non-type material. Holotype: top left and top middle. Scale bar = 0.5 mm.